Process for manufacturing dry cells



June 3, 1941. P. A. MARSAL 2,244,016

PROCESS FOR MANUFACTURING DRY CELLS Original Filed March 18, 1936vIIIIIIIIII\ INVENTOR PAUL A. MARSAL I ATTORNEY Patented June 3, 1941 fPROCESS FOR MANUFACTURING DRY CELLS Paul A. Marsal, Lakewood, Ohio,assignor to Na- .tional Carbon Company, Inc., a corporation of New YorkOriginal application March 1 8, 1936, Serial No.

69,503. Divided and this application March 30, 1938, Serial No. 198,815i 13 Claims.

This invention relates to galvanic cells and, more particularly, to aprocedure for applying an improved sealing means to so-called dry cells.The present application is a division of copending application SerialNo, 69,503, filed March 18, 1936, now Patent No. 2,169,702, issuedAugust 15, 1939.

It is important to retard or prevent the leakage and evaporation ofmoisture from dry cells, and to permit escape therefrom of gasesgenerated therein. Formerly, a relatively thick body of wax compositionwas used to seal the dry cell; and, more recently, a muchthinnerclosure, such as sheet metal, has been used instead of the wax seal. Thethinner closure usually comprises an annular disc-like cover memberwhich has its outer margin permanently and gas-tightly secured to theupper end of the zinc container elec trode, and has its inner margingas-tightly supported by the central carbon electrode. The carbonelectrode preferably is sufiiciently porous to vent gas generated in thecell and is treated with lubricating oil or other suitable compositionto prevent loss of moisture through its pores. In the smaller orso-called flashlight size of cell," the top end of the carbon electrodecarries and contacts with a'brass cap having a flange to provide abearing or support for the inner margin of the cover and for anelectrically non-conductive member which insulates the cover from thiscap and the carbon electrode. Compared with those having wax seals orclosures, the cells provided with the thin closures are stronger, moreuniform in performance and appearance, and have a considerably greateruseful space within the cell for active material, in proportion to theexternal dimensions of the cell.

In some types of cells, such as the metalsealed cells for flashlightservice, the usefulness of such extra spacehas been severely limitedbecause the flange of the brass cap is exposed inside the cell. Undercertain conditions the various salts, which partlycompose the cellelectrolyte, creep up the inside surface of the zinc can and across theinner surface of the metal cover, making contact with the cover and theflange of the brass cap and resulting in deterioration and destructionof the cell. The creepage .of

these salts is especially harmful at elevated 'temperatures andhumidities, such as are common in tropical climates. For this reason ithas been necessary to retain as an air space a considerable part of thevolume gained by the use of the thinner seal and, in some instances, toprovide special means to increase the length of the creepage path.

Accordingly, the principal objects of this invention are to overcome theabove-described objectionable features of dry cells having thin covers,especially those comprising sheet metal; to provide a cell in which asubstantial portion of the extra space, made available by the thincover, may be safely used to increase the volume of active material inthe cell; to provide a cell in which metal parts of the closure,especially the gap between such parts, are internally protected againstcontact with active material in the cell; to provide a cell which ismore effectively sealed against loss of moisture; and to provide a cellwhich will more successfully withstand deteriorationunder variousconditions of temperature. and humidity throughout the world,particularly in or near the tropics and in humid localities. These andother objects and the novel features of this invention will be apparentfrom the following description taken with the accompanying drawing, inwhich: i

Fig. 1 is a view, partly in section, illustrating a dry cell embodyingthis invention;

Figs. 2 and 3 are sectional views illustrating steps in the process ofmanufacturing the cell shown in Fig. 1;

Figs. 4 and 5 are sectional views similar to the top part of Fig. 1,illustratingother cells embodying this invention;

Figs, 6 and '7 are perspective views of the annular bodies of plasticmaterial used in manufacturing the cells shown in Figs. 4 and 5. re-

spectively;

Fig. 8 illustrates a step in another process of manufacturing a cellembodying this invention; and

Figs. 9 and 10 are views illustrating steps in other processes of makingdry cells embodying this invention.

According'to this invention, an annular body along or across its surfaceto short circuit or' otherwise damage the cell. The plastic materialpreferably covers the entire interior surface of the closure, includingthe joints between parts ofthe closure and the joints between theclosure and the carbon and zinc electrodes. However, in some instancesit is suflicient to apply the plastic material so that it bridges andinternally covers only the joint between the flange of the brass cap andthe inner margin of thecover member resting thereon, as well as thejoint between the carbon electrode and the brass cap; or only the jointbetween the cover member and the zinc can. The relatively thick solidadherent body of plastic material thus protects and insulates theinterior surface of the closure during the full life of the cell,particularly the adjoining portions of the cover and the brass cap, bypreventing access of electrolyte thereto; and said material provides anelectrolyte anti-creepage means which also more efiectively seals thecell at the joints between the closure and the electrodes, preventingloss of moisture from the cell. By this construction, deterioration ofthe cell is greatly retarded, and a considerably larger volume of activematerial may be safely used in the cell.

The several figures of the drawing illustrate the invention applied to atypical dry cell of the size used for flashlight service but theinvention is not limited to this type of cell. As shown, the

cell comprises a cylindrical zinc can or container electrode Z; acylindrical carbon electrode member C disposed centrally within andspaced from the outer electrode Z; a cylindrical body of depolarizingand active material or mix M in which the inner end of the electrodemember C is embedded; and a bibulous spacing material E between the mixM and the electrode. Z. The

spacing material E may consist of suitable paste or absorbent materialsuch as paper, and contains the complete electrolyte needed during thefull -life of the cell. A suitable electrolyte, such as an aqueoussolution of zinc chloride and ammonium chloride, may beused. Theelectrode member C preferably consists of a solid rod of porous carbontreated with a moisture repellant composition, so that gas generated inthe cell will vent through this electrode to the atmosphere butsubstantially no moisture will escape from the inside of the cell.Otherwise, the'parts just described may be of the usual or any preferredtype. An annular collar K of still paperboard or other suitable materialis disposed in the gas space G at a substantial distance above sirablyis provided with an out-turned annular flange B at its lower edge and avent hole B" opposite the top of the electrode C. The cover A mayconsist of relatively rigid but resilient ,/sheet material such asmetal, paperboard, fiberboard or molded plastic material; and as shownit consists of thin sheet iron or steel. The outer margin of the cover Apreferably is permanently and gas-tightly secured to the upper end ofthe electrode Z, as by tightly rolling or spinning the margin of thecover A over the circular edge of the can Z. The inner margin of thecover A is supported by the electrode member C, since it presses firmlyagainst an annular washer W of moisture-proof and electrical insulatingmaterial which is carried by the flange B of the cap B that is mountedon'the electrode C.

electrodes, by melting or fusing and depositing said mass into sealingposition after the closure has been secured to the zinc can. The mass Pmay consist solely of thermoplastic material which is bothmoisture-proof and electrically non-conductive and, when set, adheresfirmly to the interior surfaces of the cover and the adjoining interiorsurfaces of the electrodes. It will be seen that the plastic material Pbridges the gap between the flange B and the cover A,

thereby effectively resisting access of electrolyte salts to theseparts. In addition, the joint between the cover A and the electrode Zand -the joint between the cap B and the electrode 0 are completely andgas-tightly sealed to more effectively prevent loss of cell moisture andresist creepage of electrolyte salts through or across these joints.

Various procedures may be followed in applying the unitary body or massP to manufacture an improved cell embodying this invention. As shown inFigs. 2 and 3, before the cover A and cap B are secured in place a ringor annulardisc D of thermoplastic material is placed on the colsure ofthe cell to melt the disc D and cause it to flow over and cover theentire interior surface of the closure and the joints thereof, to'produce the adherent protective mass P. The cell is rean adherentprotective mass only to the gap between the flange B and the cover A andbetween the flange B and the electrode C, as shown at P in Fig.4. Here,a thermoplastic disc D, as shown in Fig. 6, having the same internaldiameter as, but a smaller external diameter than, the disc D, may -beused to produce the protective mass P. Similarly, it will be sufllcientin some constructions to apply a protective mass only to the jointbetween the cover A and the zinc can 2, as shown at P" in Fig. 5. Here athermoplastic disc D", as shown in Fig. 7, having the same externaldiameter as, but a larger internal diameter than, the disc D, may beused to produce the protective mass P". The masses P and P" prevent saltcreepage to the flange B and also effectively seal the outer joint ofthe closure, so that less precision in the closing operation isnecessary. The use of the protective mass P" also leaves the innermargin of the cover A free to be lifted off the washer W, to serve as anauxiliary vent to release excessive gas pressure generated in the cell.

The same general :procedure, as that descr bed in connection with Figs.2 and 3 and the use of the disc D, is followed in inserting, displacing.and using the discs D and D" to produce the masses P, P", respectively,except that the fusing heat may be more localized in applying thelatter. For example, in applying the mass P" the localized heating maybe concentrated upon the outer seam or joint of the closure and theelectrode Z.

The discs D, D and D" may consist ofany sfiuitable thermoplasticmaterial that may be fused or melted at moderately elevated temperaturesand will readily solidify at ordinary room temperatures to produce aprotective mass which is adherent after melting and solidification, iselectrically non-conductive, and resistant to moisture and creepage ofelectrolyte salt, A thermoplastic composition which has been found to besatisfactory is as follows:

Soft asphalt 5 parts by weight Montan wax 5 parts by weight Asbestine(talc) 4 parts by Weight White parafiin 1 part by Weight Tung oil 2 cc..per 100 grams of the,

above materials Other suitable materials are: a mixture of gilsoniteselects with soft asphalt; chlorinated I paraflin; ceresin wax;- amixture of rosin and rubber; and a mixture of stearic acid, tallow,candelilla wax and petrolatum.

For a typical flashlight dry cell 1%. inches diameter by 2 A incheshigh, a thermoplastic disc the cell to melt the internal thermoplasticdisc.

As shown in Fig. 3, radiant heat preferably is used and may be appliedby an electrically heated body H consisting of a ribbon of metalresistance alloy such as nichrome. A suitable spacing member H maysupport the cell at the proper distance above the heater H. An exposureof about seconds, at a distance of about one-fourth inch between thecover of the cell and the radiant body H heated to about cherry red, hasbeen found satisfactory to melt a properly located disc of the type ofdisc D. Obviously, the heating interval will vary with various factorssuch as. the nature of the thermoplastic material, the temperature ofthe cell, the type of closure, etc.

The use of the thermoplastic material in ring or disc. form affordsdistinct advantages in handling and in controlling the quantity anddis-- tribution of material. However, in some instances, e. g., for lessprecise distribution of the protective mass, thermoplastic material inloose, freely-movable pulverized or pellet form -may be placed onthe-collar K in the cell. Such pellet material R is shown in theinverted cell of Fig. 8, ready to beheated as previously describedmaterial S-of the kind already described ispoured onto the collar K justprior to the seaming or closing operation. -'I'he closure is thenquickly spun in place and the cell is quickly in-. verted. ..The moltenmateria1.then flows down and completely covers the inter-iorsurfaces tobe protected and, upon cooling to room temperature, solidifies andproduces a solid adherent protective mass similar to the protective massP of Fig. 1.

In some instances, instead of using a thermoplastic material it isdesirable to use materials which will polymerize to producethedesiredadherent coating or protective mass. As shown in Fig. 10, asuitable polymerizable material T may be deposited or poured onto thecollar K just prior to the closing operation. After the closure has beensecured in place, the cell is inverted and aged in the inverted positionuntil the polymerizing material has solidified to produce a protectivemass similar to the coating or mass P of Fig. 1. For this purpose it hasbeen found satisfactory' to use a tung oil which is polymerized byferric chloridea practical formula being:

tung oil, grams; ferric chloride, 6 grams ;and acetone, 2 grams. If thematerials which form the protective mass react too quickly, they may bekept separate until after the cell has been closed and inverted. Thismay be done by applying one of the reactive constituents to the innersurface of the cover, as indicated at U in Fig. 10. When the cell hasbeen closed and is inverted, the other reactive constituent, such as T,will be deposited upon the constituent U, whereupon a reaction willoccur to produce a protective mass similar to the mass P of Fig. 1.

While numerous embodiments of this invention are disclosed herein, itwill be understood other variations and changes are possible withoutdeparting from the principles of the invention or sacrificing itsadvantages.

Whatisclaimed is:

1. In a process of producing a dry cell in which, during assemblingthereof, a central carbon electrode is inserted into a metal containerelectrode, active material and a complete electrolyte are disposedwithin said metal container electrode between the latter and saidcentral carbon electrode, 'and a cover member has one margin thereofpermanently secured to said metal container electrode and has anothermargin thereof supported by said central carbon electrode, the steps ofloosely disposing, Within said dry cell above said electrolyte andactive material and prior to permanently securing said cover member tosaid metal container electrode, material adapted to solidify into amoisture-repellent, electrically non-conductive andelectrolyte-creepageresistant composition; inverting said cell, afterpermanently securing said cover member to said metal containerelectrode, to displace said material a-djacent to the inner side of saidcover member; and causing said material to flow against and solidify inpermanent contact with an annular interior surface portion of said cover.member and an adjoining annular interior surface portion of at leastone of said electrodes, so as to produce an annular solidified mass ofsaid composition which during the full life of the cell permanentlyinternally bridges and seals the joint between said surface portions andresists creepage of electrolyte to and across said joint.

2. Process of sealing a dry cell and inhibiting creepage of electrolytematerial to the cell closure and to the joints between said closure andthe cell electrodes, said process including the step of introducingwithin the cell a freely-movable mass of solid thermoplasticwater-repellent material, rigidly securing a cell closure to the cell,and thereafter moving the said material into contact with the closureand melting the said material, thereby covering the interior of saidjoints and the entire interior surface of said closure with an adherentsealing composition adapted to resist creepage of electrolyte material.

3. A process of making a galvanic cell, which includes the steps ofdisposing freely movable,

moisture-repellant, electrically non-conductive,

thermoplastic material in solid form within said cell; securing aclosure member to the open top of said cell; inverting said cell todisplace'said material into contact with an internally exposed portionof said closure member; andheating said 1 material to melt the same andcause it to flow over and cover at least a portion of the interiorsurf-ace of the closure.

4. In a process of producing a dry cell in which, during assemblythereof, an electrode member is inserted into a container electrode,active material is disposed within the said container electrode betweenthe latter and the said electrode member, and a cover member hasone'margin thereof permanently secured to said .con-' tainer electrodeand has another margin thereof supported by said electrode member, thestep of disposing, within the container electrode above the said activematerial and prior to permanently securing the cover member to thecontainer electrode, an annular disc of moisture-repellent andelectrolyte-creepageresistant thermoplastic material, said annular dischaving an external diameter slightly less than the internal diameter ofsaid container electrode and an internal diameter considerabily greaterthan the diameter of said electrode member, together with the steps,

subsequent to permanently securing the cover member to the containerelectrode, of inverting the cell and then heating the thermoplasticmaterial and flowing the resultant molten material upon theinterior-surface portion of the cover member adjacent the containerelectrode and the margin thereof permanently secured to said conteinerelectrode and has another margin thereof supported by said electrodemember, the'step of disposing, within the container electrode above thesaid'actlve m-aterial'and prior to permanently securing the cover memberto thecontainer electrode, an annular disc of moisture-repellent andelectrolyte-creepage-resistant thermoplastic material; saidannular dischaving an internal diameter slightly greater than the diameter of saidelectrode member and an external diameter considerably less than theinternal diameter ofsaid container electrode, together with. the steps,subsequent to permanently securing the cover memberto the containerelectrode, of inverting. the cell and then heating the thermoplasticmaterial and flowing the resultant molten materlalupon the interiorsurface portion of the cover member adjacent said electrode member andthe adjacent interior surface portion of said electrode member, therebyforming an adherent coating upon said interior surface portions.

6. In a process of producing a dry cell in which, dui'ing assemblythereof, an electrode member is inserted into a container electrode,active material is disposed within the said container electrode betweenthe latter and the said electrode member, and a metal cover member hasone margin thereof rigidly secured to said container electrode and hasanother margin thereof supported by said electrode member but insulatedtherefrom, the step of loosely disposing moistureresistant electricallynon-conductive thermoplastic material in solid form within the containerelectrode above the said active material prior to securing the covermember to the container electrode, together with the step, subsequent tosecuring the cover memberto the container electrode, of concurrentlyheating the cover member and the thermoplastic material and flowing theresultant molten material upon the interior surface of the cover member,thereby forming an adherent coating upon thelatter.

7. In a. process of producing a dry cell in which, during assemblythereof, an electrode member is inserted into a container electrode,active material is disposed within the said container electrade betweenthe latter and the said electrode member, and a metal cover member hasone margin thereof rigidly secured to said container electrode and hasanother margin thereof Supported by said electrode member but insulatedtherefrom, the step of loosely disposing moistureresistant electricallynon-conductive thermoplastic material in solid form within the containerelectrode above the said active material prior to securing the covermember to the container electrode, together with the step, subsequent tosecuring the cover member to the container electrode, of concurrentlyheating the cover member and thermoplastic material and flowing theresultant molten material upon the interior surface of the cover memberand adjacent portions of the container electrode, thereby forming anadherent coating upon the said interior surface,'

r therefrom, the step of loosely disposing moistureresistantelectrically non-conductive thermoplastic material in solid form withinthe container electrode above the said active material prior to securingthe cover member to the container electrode, together withthe step,subsequent to securing the cover member to the container electrode, ofconcurrently heating the cover member and thermoplastic material andflowing the resultant molten material upon the interior surface of thecover member and adjacent portions of the said electrode member, therebyforming an adherent coating upon the said interior surface and bridgingthe joint between the cover and the said electrode memben 9. In aprocess of producing a dry cell in which,

duringassem-bly thereof, an electrode member is inserted into acontainerelectrode, active mate'- rial is disposed within the saidcontainer electrode between the latter and the said electrode member,and a metal covermember has one margin thereof rigidly secured to saidcontainer electrode and has another margin thereof sup- ;ported by saidelectrode member but insulated therefrom, the step of loosely disposingmoistureresistant electrically non-conductive thermoplastic material insolid form within the container electrode above the said active materialprior to securing the cover member to the container electrode, togetherwith the steps, subsequent to securing the coverlmember to the containerelectrode, of inverting the cell to deposit the said thermoplasticmaterial on the inner surf-ace of the cover member, and thereafterapplying heat to at least a selected portion of the cover member and tothe thermoplastic material, thereby melting the said material andforming an adherent coating thereof upon the said surface of the coverform of a body adherent to the said inner surface of the closure.

12. In a .process of producing a dry cell in which, during assemblythereof, a central electrode is inserted into a container electrode,electrolyte and active material are disposed within said containerelectrode-between the latter and said central electrode, anda covermember has one margin thereof permanently secured to said member andadjacent portions of the container electrode and electrode member, andthereafter discontinuing the said heating whereby the molten materialsolidifies while maintaining the I tainer electrode; pouring a moltenmoisture-repellent and electrolyteecreepage-resistant mate-" rial ontosaid collar, said material being capable of existing olid form under theconditions of use of the cell; quickly securing a closure to the opentop of said cell; inverting said cell to displace said material intocontact with the interior surface portion of said closure and adjoininginterior surface portions of said electrode memher and said containerelectrode; and retaining said cell in its inverted position until saidmaterial solidifies in contact with said interlor surface portions. r

- 11. Process of making a galvanic cell, which includes the stepsofdisposing within an opentop cell a mixture of chemically reactivematerials adapted to react and form a solidiflable,

electrically non-conductive, moisture-resistant composition within saidcell, securing a closure to the open top of said cell; inverting saidcell to displace said composition onto the interior surface ,of saidclosure and initiating reaction between thesaid materials, andcompleting the said reaction while maintaining the cell inverted,thereby solidifying such reacted materials in the container electrodeand has another margin thereof supported by said central electrode thesteps of disposing thermoplastic material within said containerelectrode above said electrolyte and active material and prior topermanently securing said cover member to said container elec-. trode,such thermoplastic material being moisture repellent and resistant toelectrolyte creepage; thereupon, but after said cover member has beenpermanently secured to said container, inverting the cell; and thenheating said thermoplastic material to melt the latter and flow suchmolten material into contact with an interior surface portion of saidcover member and an adjoining interior surface portion ofone of saidelectrodes,

, steps of disposing, wi'

3 cover member has been permanently secured to said container electrode,inverting the cell to displace said material into contact with saidcover whereby such molten material, upon cooling and solidification,internally bridges and sealsrthe joint between such surface portions andresists creepage of electrolyte to and across said joint.

. 13. In a process of producing a dry cell in which, during assemblythereof, an inner electrode is inserted into a metal containerelectrode, electrolyte and active material are disposed within saidcontainer electrode between the latter and said inner electrode, andametal cover member has one margin thereof permanently secured to saidcontainer electrode and has another margin thereof supported b saidinner electrode, the u said container electrode above said activematerial and prior to permanently securing said cover member to saidcontainer electrode,'a displaceable body of moisturerepellent andelectrolyte-creepage-resistant thermoplastic material; thereupon, butafter said member; then heating said cover member and said thermoplasticmaterial to melt the latter. and flow such molten material into contactwith an interior surface portion of said cover memher and an adjoininginterior surface portion of one of said electrodes; and finallypermitting such molten'material to cool andsolidify while the cellremains inverted, whereby said material internally bridges and seals thejoint between creepage of elecsuch surface portions and resists trolyteto and across said joint.

- PAUL A. MARSAL.

